Chromium complexes of fluorocarboxylic acids



United States Patent CHRONIIUM COIVLPLEXES OF FLUOROCAR- BOXYLIC ACIDS Kermit S. La Fleur, Union, S.C., assignor to Deering Milliken Research Corporation, near Pendleton, Oconee County, S.C., a corporation of Delaware No Drawing. Application December 14, 1953 Serial No. 398,203

5 Claims. (Cl. 260-438) This invention relates to compositions suitable for rendering surfaces oil repellent and methods for their application.

The new compositions of this invention may be applied to surfaces of substantially all types to render them oil repellent and is particularly applicable to textiles and the like. Textile materials during the course of their manufacture frequently and as a rule become spotted with oils and removing these oil stains is an expensive and time consuming problem that plagues substantially every textile manufacturer. Of course, after the textile materials are manufactured into clothing or the like, they are frequently stained or spotted with oil by the wearer and this results in an objectionable appearance and necessitates cleaning. It can be seen, therefore, that an oil repellent textile material would be advantageous to both the manufacturer of textile materials and the ultimate consumer.

According to this invention a surface is made oil repellent by applying thereto a Werner complex of trivalent chromium and a fluorinated carboxylic acid. In many instances, the surface is thereby also made water repellent so that one can achieve the seemingly impossible feat of rendering a surface both oil and water repellent. When properly applied, the coating displays excellent resistance to both washing and dry cleaning so that a single coating can serve both the manufacturer and the ultimate consumer.

It has been previously disclosed that a Werner complex of chromium and a carboxylic acid having more than carbon atoms could be employed to render textiles water repellent and the Werner complexes of this invention are generally similar to those which have been previously employed in water proofing except that in the preparation of the new complexes of this invention there is employed, in place of a simple aliphatic carboxylic acid, a fluorinated acid having at least one of the hydrogens replaced by fluorine. While the formulae of the Werner complexes of chromium with carboxylic acids have not been definitely established with complete certainty, these compounds are believed to be best represented by the following structural formula:

wherein X represents an anion and R represents the residue of a carboxylic acid. In the case of this invention, R would represent a fluorinated aliphatic or cycloaliphatic group.

Fluorinated carboxylic acids suitable for use in preparing the new Werner complexes of this invention are, for the most part, well known compounds and are prepared by methods well known to those skilled in the art. A preferred class of carboxylic acids for use in the preparation of the new Werner complexes are the perfluoro-fatty acids prepared by electrochemical fluorination of the corresponding hydrocarbon acid or anhydride and capable of being represented by the formula C F C0OH. Complexes prepared from such acids offer the maximum degree of oil repellency, excellent water repellency and, because of the availability of the free acids, are readily prepared. The corresponding perfluorocycloalkyl carboxylic acids of the formula C F COOH are, in most instances, equally satisfactory. Complexes prepared from perfluoroacids, however, suffer the disadvantage that they are somewhat less stable than complexes prepared from weaker acids and in the presence of anions of only slightly ionized carboxylic acids, the perfluoroacid in the complex tends to be replaced to some extent by the weaker acid.

It is not necessary, however, for the aliphatic portion of the molecule to be completely fluorinated in order that the acids be satisfactory for use in this invention and, in fact, complexes formed from partially fluorinated acids, in some instances, are exceedingly advantageous. It would appear, however, that better results are obtained when employing the partially fluorinated acids if the fluorine atoms are on or near the terminal carbon atom or at least as far removed from the carboxyl group as possible. in some instances it will be found that one fluorine atom on the terminal carbon atom has as much or more effect as two fluorine atoms on the alpha carbon atom next to the carboxyl group and, in addition, complexes prepared from such ac1ds are more stable. Even though a single fluorine substituent on a terminal carbon atom of the aliphatic chain has considerable effect, best results are obtained where there is a plurality of fluorine substituents and complexes prepared from aliphatic acids having a terminal CF group are preferred.

While the aliphatic portion of the carboxylic acid in a new Werner complex of this invention is preferably a carbon chain, the aliphatic chain may, if convenient, also contain ether linkages or other divalent connecting groups. In certain instances, compounds containing ether linkages or other divalent connecting groups are more readily prepared than are the corresponding simple fluorinated acids and it is an advantage of the invention that acids having such linkages can be readily employed. Complexes prepared from carboxylic acids having substituent groups, and in particular keto oxygen, are also often advantageous for the same reason. It is difficult, in some instances, to prepare acids having terminal CF groups by direct fiuorination although the corresponding acids having a carbonyl connecting group may be readily prepared. Acids having substituent groups with readily replaceable hydrogen as illustrated by OH, NH and COOH can also be employed in preparing the new Werner complexes of this invention although their use is not generally advantageous for the reason that the presence of such groups, in many instances, introduces side reactions during the coating operation.

The new Werner complexes of this invention are prepared by methods analogous to those previously employed for preparing Werner complexes with the simple carboxylic acids although in some instances special precautions must be observed. A method generally suitable for preparing the new compounds of this invention comprises partially hydrolyzing chromic chloride hexahydrate with a basic hydroxide to form a basic chromic salt in accordance with the following equation:

The basic chromic salt can then be reacted with a fluorinated carboxylic acid as illustrated by the following equation:

While the Werner complex is represented in this and other equations in the specification as being devoid of water of hydration, it is not meant to imply that the complex is incapable of being associated with water of hydration and in some instances it i's-probable that the complex actually is a hydrate.

A second method suitable for preparing complexes of high boiling acids comprises simply mixing the acid with chromic chloride hexahydrate and fusing the mixture according to the following equation:

This method is not usually advantageous for preparing complexes of the perfiuoroacids as there is a tendency for the strong perfluoroacid to be replaced in the complex by the acetic acid produced by the reaction.

The new complexes of this invention are preferably applied to the surface to be treated from aqueous solution since in order for the surface coating to be reasonably permanent, it is necessary for the complex to undergo a measure of hydrolysis. Of course the complex can be applied from a hydrous organic solvent such as ethyl alcohol if desired although this procedure suffers from the disadvantages inherent in the use of organic solvents. When in the presence of an aqueous solvent, the Werner complexes of this invention tend to hydrolize to form a basic complex wherein the chromium atoms in the complex are substituted with two hydroxyl groups in each instance. These hydroxyl groups are quite reactive and the basic complex tends to react with itself with the resulting formation of Cr-O-Cr linkages and insoluble high molecular weight polymers. This results in the material becoming permanently affixed to even nonreactive surfaces such as those presented by glass, metals and the like. If the surface being treated contains reactive groups such as SO3H, OH, NHZ, CONHZ, or COOH groups, the basic complex will in addition react with these to become permanently bonded to the surface. This characteristic results in the new complexes being especially adapted to treat materials such as those formed of cellulose or cellulose derivatives, silk, wool, nylon, and the like.

The treating solution can be of any desired concentration and can for example contain from about 0.1% to of the chromic complex with the optimum concentration depending upon the surface to be treated. .Solutions of the chromic complexes of this invention are generally acidic in nature and if the surface to be treated is sensitive to acid solutions, the pH of the solution can be raised by the careful addition of a suitable basic material as illustrated ammonium hydroxide; however, since raising the pH of the solution tends to increase the rate at which the complex is hydrolized and the rate at which the resulting basic complex polymerizes, care should be exercised to retain the pH of the treating solution at all times more acidic than about pH 6.

The treating solution can be applied to the surface to be rendered oil repellent in any suitable manner such as by spraying, brushing or by dipping the surface into a quantity of the solution. In treating textiles and similar materials a preferred procedure comprises. passing a length of the material into a treating bath containing the desired concentration of complex and then through squeeze rolls to adjust the liquid pickup of the material. The pickup should be adjusted so that the material con tains sufficient solution to result in there being deposited on the material at least 0.1% by weight of the complex and preferably at least about 0.2% by weight of the complex. On the other hand, if more than about 1% of the complex is deposited on the material there is obtained a noticeable discoloration. In instances where this discoloration is not objectionable, there can be applied up to 20% or more of the complex with satisfactory results. It will be appreciated that the above figures are for textiles or other materials having a large surface area and that if one is treating a relatively smooth impervious surface, much smaller quantities of the complex need be applied. For example surfaces of molded nylon articles can be rendered measurably oil resistant by applying as little as .02 ounce of complex per square yard of surface.

Once applied to the surface, the complex is self-curing and will harden to an insoluble state in one to two days at room temperature. If possible, however, it is generally advantageous to dry the treated surface at a temperature of at least about 200 F. since this insures reasonably complete hydrolysis of the complex and initiates the process of polymerization.

The invention will now be illustrated by the following specific examples in which all parts are by weight unless otherwise indicated:

EXAMPLE I In an open reaction vessel there is melted 266 parts by weight of chromic chloride hexahydrate and to the molten material there is then added 358 parts by weight of perfluoromyristic acid CwPzqCOOH (I & E Cem. 43, 2332). The mixture is maintained at a temperature of about 160 C. for 20 minutes and then allowed to cool. The reaction product is dissolved in approximately two liters of warm ethanol to give a dark green slightly turbid solution and the ethanol solution is cooled to approximately 5 to 10 C. and filtered to remove insoluble material. The ethanol solution is then evaporated to dryness to give approximately 370 parts by weight of a completely water soluble dark green product.

Approximately 300 parts by weight of the above product is dissolved in about 700 parts by weight of isopropyl alcohol and to 10 parts by weight of the isopropyl alcohol solution there are added to parts by weight of distilled water. A small sample of an eight ounce woolen material is immersed in the aqueous solution and then passed through squeeze rolls to give a liquid pickup of approximately The cloth sample is then dried at room temperature and allowed to stand for three days at the end of which time the sample is found to be highly repellent to both oil and water stains.

Equally satisfactory results are obtained when an equivalent quantity of perfluorocaproic acid, perfluoropalmitic acid, perfluorolauric acid, perfluorocapric acid, perfluorocaprylic or perfiuorostearic acid is substituted for the perfiuoromyristic acid employed above. Optimum oil repellency with excellent water repellency is generally obtained with a chromic complex prepared from perfiuorocapric acid.

EXAMPLE 11 Several aqueous treating solutions of varying concentrations are prepared as above except that a Wernertype chromic complex of perfiuorocaproic acid is substituted for the complex of perfluoromyristic acid. Several samples of an 8 ounce wool-polyacrylic material are treated with each of the solutions by immersing the sample in the solution, passing the thoroughly Wetted sample through squeeze rolls and drying at a temperature of from about 00 to 250 F.

Resistance to Wetting by oil is determined by applying ten drops of mineral oil, vegetable oil (soybean oil) or animal oil (oleic acid) to the treated fabric with a medicine dropper, allowing the drops to remain for three hours, draining ofi the excess with the corner of a blotter and finally passing the samples through a wringer between blotters and weighing. Resistance to Wetting by water is determined by standard spray rating technique.

In a series of tests performed as above it was found that as little as 0.3% by weight of complex on the fabric sample was sufficient to give both excellent water repellency and excellent oil repellency. The actual test results are given in the following table:

Thus it will be seen that as little as 0.15% by weight of the complex on the cloth surface resulted in fair Water repellency and considerable oil repellency and that almost complete resistence to both oils and water can be obtained with as little as about 0.3% by weight of the chromic complex applied to the textile material.

EXAMPLE III Into a suitable reaction vessel equipped with a reflux condenser there is placed 40 parts by weight of chromic chloride hexahydrate, dissolved in 215 millimeters of methanol, and 6 parts by weight of sodium hydroxide dissolved in 20 parts by weight of methanol. The resulting mixture is refluxed for 20 hours, cooled and then filtered to remove insoluble material.

To 50 parts of the filtered methanolic solution there is added 1.6 parts by weight of perfluoroacetic acid and the resulting mixture refluxed for one hour. The mixture is cooled to about 10 C. and filtered to remove insoluble material. The mixture is then evaporated to dryness to give approximately 6 parts by Weight of a dark green product which is then dissolved in 16 parts by weight of isopropyl alcohol.

To 50 parts by weight of distilled water there is added 5 parts by weight of the above isopropyl alcohol solution. A small sample of cotton shirting is then immersed in the aqueous solution and squeezed to give a pickup of approximately 50%. The cloth sample is dried at a temperature of approximately 250 C. and allowed to remain at room temperature for three days at the end of which time it is found to have a measurable oil repellency.

The remaining methanolic solution above is divided into 4 aliquot portions of approximately 50 parts each. To the first there is added 5.7 parts by weight of perfiuorocyclohexane acetic acid (I & E Cem. 43, 2332); to the second there is added 2.4 parts by Weight of 4-trifluoro- 3-oxobutanoic acid (Bull. classe. sci. Acad. Roy. Belg. 12, 689); to the third there is added 2.25 parts by weight of 3hydroxy-4-trifluorobutyric acid (JACS 70, 143); and

to the fourth there is added 2.6 parts by weight of 2,3- tetrafluorocyclobutanecarboxylic acid (U.S. Patent 2,441,- 128). Each of the four samples is then refluxed for one hour, cooled and filtered. The four samples are then evaporated to dryness and the residues in each instance dissolved in approximately 30 parts by weight of isopropyl alcohol. The isopropyl alcohol solutions are then diluted approximately 10 fold with distilled water and cloth samples treated with each of the solutions as above. In each instance the treated cloth sample displays an appreciable measure of oil repellency.

EXAMPLE IV Into a suitable reaction vessel equipped with a reflux condenser there is placed a solution containing 64 parts by Weight of 8,9-difluorostearic acid (Ann. 506, 20) dissolved in approximately 600 parts by Weight of anhydrous carbon tetrachloride and to this solution there is added 14 parts by Weight of anhydrous ethyl alcohol. The mixture is brought to boiling and there is slowly added over a period of two hours a solution of 62 parts by weight of chromyl chloride dissolved in 250 parts by weight of anhydrous carbon tetrachloride. Refluxing is continued for an additional 30 minutes at the end of which time the carbon tetrachloride solvent is evaporated to give a dark green residue. The residue is purified by dissolving in a minimum quantity of warm anhydrous methanol, cooling in mixture to about 10 C. and filtering to remove insoluble impurities. The methanol solvent is then evaporated to give approximately parts by weight of purified product.

Two parts by Weight of the above product are dissolved in 10 parts by weight of isopropyl alcohol and the resulting solution added to parts by weight of distilled water. A small sample of a wool-polyester (Dacron) fabric is immersed in the aqueoues solution and squeezed to give a pickup of approximately 100%, the sample dried at 200 F., and allowed to remain at room temperature for two days. At the end of this time the treated fabric displays an excellent resistance to Water and a measurable resistance to oil stains.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. As a new oil-repellent composition of matter, a Werner-type complex of trivalent chromium and a fluorinated carboxylic acid represented by the formula CF Z-C,,H ,,COOH wherein Z represents a divalent connecting radical selected from the group consisting of CH -CO-, O, and CHOH radicals and n represents an integer of from 1 to 15.

2. A composition as claimed in claim 1 wherein said acid is an acid of the formula CF COC H COOH.

3. A composition as claimed in claim 1 wherein said acid is 4-trifluoro-3-oxobutanoic acid.

4. A composition as claimed in claim 1 wherein said acid is an acid of the formula CF CHOHC H COOH.

5. A composition as claimed in claim 1 wherein said acid is 3hydroxy-4-trifluorobutyric acid.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AS A NEW OIL-REPELLENT COMPOSITION OF MATTER, A WERNER-TYPE COMPLEX OF TRIVALENT CHROMIUM AND A FLUORINATED CARBOXYLIC ACID REPRESENTED BY THE FORMULA CF3-Z-CN-H2NCOOH WHEREIN Z REPRESENTS A DIVALENT CONNECTING RADICLA SELECTED FROM THE GROUP CONSISTING OF -CH2-, -CO-, -O-, AND -CHOH- RADICLAS AND N REPRESENTS AN INTEGER OF FROM 1 TO
 15. 